Tiers are simply "banlists" for Pokémon in order to balance a given metagame. Stronger Pokémon are banned to higher tiers, giving weaker Pokémon a chance to be used in a competitive environment. For the most part, tiers can be separated into 4 categories: Ubers, OverUsed, UnderUsed, and NeverUsed. Ubers is more of a banlist than a tier, since everything too strong for other tiers is placed there.

Pokémon are separated into tiers using two methods - statistics and power. Power tends to be classified of how "broken" a Pokémon is, or how much it "overcentralizes" the metagame. An example of a broken Pokémon would be Mewtwo - who has been banished to Ubers ever since the first generation of Pokémon. In the case of the former, statistics, let us look at Garchomp; which is the prime example of a Pokémon overcentralizing the metagame. In 4th Gen (DPP) OU, every team was essentially required to carry a few Pokémon who could take care of Garchomp. Overcentralization is often cited as the reason for Garchomp being relegated to ubers in Generation 4.

Tiers are generally decided with input from the community, either via the process of discussion on the forums or by a general vote. However, in some cases, tiers are determined by a small group of people. Reasons for doing this will vary, but in the case of tiers such as UU or LU in Generation 5; it is because the metagame is still being settled. To debate every single Pokémon would be detrimental and time-consuming. Ultimately, we try to make the best decision for the users but it is impossible to please everyone. The best way to help shape our tiers is to participate in the discussions on the forums and in the votes that do come up.

Important Note: We do not follow Smogon's tiers in many instances.

Tiers In General:Ubers - Pokémon that are too powerful for any other tier. Keep in mind that Uber Pokémon are not classified by how powerful they are in the Uber metagame, but by how powerful they are in OU (and other) metagames.OverUsed (OU) - The most commonly played tier, no matter which Generation you are in. All Pokémon are allowed, except the ones on the Uber banlist.UnderUsed (UU) - Uber and OU Pokémon are not allowed in this tier. It is to give lesser-used and weaker Pokémon a chance to flourish. Fairly popular across most Generations, but not played as much as OU.NeverUsed (NU) - Uber, OU, and UU Pokémon are not allowed in this tier. The least used and weakest Pokémon play here, and some of them will surprise you at how well they perform in their unique environment. Usually not the most popular metagame, but is played.

Tiers By Generation:Generations 4 & 5 introduced new tiers and there are even unique metagame tiers. We will cover these here.

Fifth Generation (Pokémon Black/White)

Dream World - A new feature in Pokémon Black/White which allows you to catch Pokémon which may have different abilities than usual, have special moves, or carry rare items. These Pokémon must be released by Nintendo in order for the player to catch them ingame. On Pokémon Online, the Dream World tiers are where a metagame is completely simulated. This means that Pokémon can be used with their unique Dream World abilities, moves, and items - even if they have not been released by Nintendo. Please note that Event Moves are not coded in any part of the data tables in the cartridges, thus these special moves are not allowed on the Dream World tier until they are confirmed by Nintendo for a future event.Wifi - This is classified as the 'standard' tier. Only released special abilities, moves, items, and Pokémon can be used. Additionally, the Wifi Clause is in effect - which is a new ingame mechanic that allows players to see each other's teams before the battle starts and re-order Pokémon as desired.Clear Skies - Formerly named the Weatherless tier, this is where weather is nullified. If you're tired of seeing Sun, Rain, Sand, or Hail teams in Wifi/Dream World then this is the tier to play!1v1 - One Pokémon per team. Banned Pokémon, moves, and items can be found in the Gen 5 Tier List.Monotype - Your team can only consist of Pokémon belonging to the same type category. See this thread for full details.Triples - Three Pokémon against three Pokémon on the field at the same time.Doubles - Two Pokémon against two Pokémon on the field at the same time.BW Cup - Only Unova Pokémon can be used.LC (Little Cup) - First stage evolution Pokémon. See 5th Gen Tier List for exact details.LU (Lesser Used) - The first Generation to have a LU tier. This is in-between UU and NU, and is established by usage percentage as opposed to power.

Fourth Generation (Pokémon Diamond/Pearl/Platinum)

1v1 - One Pokémon per team. Banned Pokémon, moves, and items can be found in the Gen 4 Tier List.No Hazard - Same as Gen 4 OU, except without entry hazards. (Spikes, Stealth Rock, Toxic Spikes)Doubles - Two Pokémon against two Pokémon on the field at the same time.LC (Little Cup) - First stage evolution Pokémon. See 4th Gen Tier List for exact details.

Advance/Third Generation (Pokémon Ruby/Sapphire/Emerald)

Doubles - Two Pokémon against two Pokémon on the field at the same time.

GSC/Second Generation (Pokémon Gold/Silver/Crystal)

There is no NU tier due to a lack of Pokémon.

VGC - Video Game Championship Series

These are the video game tournaments hosted annually, by Nintendo. For more details, you can see http://pokemonvgc.com/ but we will sum up the rules for each tournament here. So far, all VGCs have been Level 50 (or below, using Auto-Level) Pokémon in Double Battle mode. Additionally, Species Clause and Item Clause has been in effect for each one; as well as a ban on illegal moves. We emulate the same rules as in VGC, except for the rule about changing Pokémon/items from match to match - provided you are not in a VGC tournament that forbids such activity.